This invention relates to a well treating process for reacting acid-reactive material in and around a well within a subterranean reservoir formation with at least one alpha-hydroxysulfonic acid. More particularly, the invention relates to a well acidizing process in which the rate of reaction of an aqueous strong acid can be retarded enough to allow relatively deep penetration into a reservoir formation containing acid-reactive material.
Numerous methods and compositions have been proposed for reducing the rate of acidization reactions with aqueous solutions of strong acids such as hydrochloric acid or mixtures of hydrochloric and hydrofluoric acids. The prior proposals have included: dissolving or emulsifying an acid or acid-forming material in a non-aqeous liquid; forming an acid within a water-containing remote location, such as a subterranean reservoir, by means of a relatively slow hydrolysis of an organic halide or ester; dissolving a water-thickening material in an acid to reduce the rate at which the acidic component can diffuse into contact with acid-reacting material; and the like.
For example, U.S. Pat. No. 3,889,753 by E. A. Richardson suggests acidizing silicious material by contacting it with an aqueous solution of a fluoride salt, a weak acid, and a weak acid salt in proportions which maintain a significant but low concentration of hydrogen fluoride in the solution. U.S. Pat. No. 4,122,896 by R. F. Scheuermann, E. A. Richardson and C. C. Templeton, suggests acidizing a carbonate reservoir by injecting an aqueous solution of a chlorocarboxylic acid salt so that the rate of acidization is limited to the rate at which an acid is formed by the hydrolyzing of the chlorocarboxylate ions. The disclosures of those patents relative to utilizations of aqueous strong acid solutions having relatively slow rates of reaction are incorporated herein by reference.
Numerous reactions of aqueous solutions containing a sulfite and aldehyde are known. For example, in U.S. Pat. No. 4,508,171, an aqueous alkaline solution containing a sulfite and an aldehyde are injected into an oil containing subterranean reservoir to react in situ with the oil to form a surfactant for aiding the displacement of the oil toward a production location. U.S. Pat. No. 4,395,356 by L. H. Slaugh and C. L. Willis relates to removing catalyst residues from a polybutene polymer dissolved in a hydrocarbon solvent by contacting the solution with an aqueous solution of an alpha-hydroxysulfonic acid prepared by reacting a carbonyl compound with sulfur dioxide and water. U.S. Pat. No. 4,396,761 by C. L. Willis and L. H. Slaugh relates to removing hydrogenation catalyst residues from conjugated-diene polymers by contacting solutions of them with a similarly prepared alpha-hydroxysulfonic acid. An acidulation process for treating phosphate rock described in Chem and Engineering News, Sept. 6, 1976, involves reacting the rock at room temperature with a mixture of acetone, sulfur dioxide and water in a manner causing the phosphorous to dissolve (mainly in the form of dicalcium phosphate) for recovery as a filtrate while leaving a filter cake containing calcium alpha-hydroxy-2-propane sulfonate from which sulfur dioxide and acetone can be recovered by heating.
In such extracting and acidulating processes the use of the hydroxysulfonic acid prepared by the in situ reaction between SO.sub.2 water and a carbonyl compound is advantageous because such reactants form a solution in which, even at ambient temperatures, the water, SO.sub.2 and the carbonyl compound quickly form an equilibrium between them and an alpha-hydroxysulfonic acid. The reaction is one in which an increase in temperature shifts equilibrium by increasing the proportion of unreacted SO.sub.2 and carbonyl compound, whereas an increase in SO.sub.2 pressure shifts the equilibrium toward the production of the sulfonic acid.